how can あなた tell if a boy is still a virgin?

Ask him!

In a relationship, あなた should be able to talk about everything, especially if あなた have no experience.

So be open about your experiences and ask him about his.

Take your clothes off and wait for reaction.

Ask him how many he's slept with. If he says 3, he's a virgin.

It's hard to really tell. My best assumption is, it could be their reaction to certain things または they're not experienced enough to make sex good at all. I knew all my partners were not virgins, so I can't say.

People who are chilled out または rebel types are もっと見る likely to be virgins, I would say. または people who are religious または innocent.
I'm 21, I refused to have sex until I find the right girl, because I only want to have one sexual partner in my life. I don't want my mind cluttered with memories of other girls, because my brain is full of the memories of my life.

He brags about not being one

There is NOT a way, nope, no, あなた can ask. I think most of the time people または guys do answer it honestly, but they can lie. あなた would only know if あなた could discern in how they answered -like if they really sounded braggy または full of poop, lol -maybe. There just is no way to know.